I've been using Starlines & Winchester primers, with zero problems for years.

Shadow you used the term leakage ? Were you seeing powder ?

No, not powder.  When the cartridges were fired and later examined, you can see black soot, that passed between the primer and the primer pocket.  This could have been just looser pockets on those brass.  I use mostly used brass (reconditioned) for testing, some have been shot several times, hand priming does allow for the touchy / feely sensations of the fit when priming.

Thanks for the info. You learn something new everyday that's why I love this site.